This invention relates to the shape of detergent tablets for automatic dishwashers. More particularly, this invention relates to tablets that can be positively dispensed from the dispensing holder of an automatic dishwasher upon the holder being activated.
Detergent tablets have been developed for use with automatic dishwashers. In order to be positively dispensed into the washer tub each time that the detergent tablet holder is activated, the tablet has to be of a particular shape. This is the case since not all tablet shapes will be dispensed each time the detergent holder compartment is activated and opened. It is important that the tablet not interfere with the opening of the detergent holder and that it be dispensed down into the wash water in the wash tub. If left in the detergent holder compartment, the likelihood is that the tablet will only be partially dissolved. Only some of the detergent will get into the wash tub and be used to wash the dishes. The amount that remains in the holder will be wasted. The net result is that the dishes in most instances will not be effectively washed. Not all of the soils will be removed. There will be a residue soils layer on at least part of the surfaces of the dishes.
One reason that there is difficulty in the dispensing of tablets into the wash tub of an automatic dishwasher is that the detergent dispensers were designed for use with powder and gel detergents. Each of these will flow into the wash tube when the detergent holder is opened. Any residual amount in the detergent holder is quickly dissolved by the water being splashed in the wash tub. The detergent holder will be clean after each wash. However, when a detergent tablet hangs up in the detergent holder and not be dropped into the wash tub, it usually will be dissolved only partially.
The prior art of detergent tablet shapes is set out in several patents, one of which is U.S. Pat. No. 5,133,892. There is disclosed a cylindrical tablet having three concentric layers. This patent is directed to the timed release of the different concentric layers. The different substances of these concentric layers are released sequentially. In U.S. Pat. No. 3,557,003 there is disclosed a cylindrical tablet that has beveled edges. The tablet also has passages for the release of gas as wash water penetrates the tablet. U.S. Pat. No. 3,423,322 also discloses a cylindrical detergent tablet that has beveled edges. This tablet is stated to have a high compressive strength.
The problem that was confronted was to produce a dishwasher detergent tablet in a shape where it will be readily and positively dispensed from a detergent holder and into a dishwasher tub, and that will contain a high amount of detergent with regard to the dimensions of the tablet. Each time that the detergent holder opens, the tablet should fall into the water in the wash tub. This problem is increased due to the different size and shape detergent holders on different brands of automatic dishwashers. This problem is solved by the dishwasher detergent tablets of the present invention. It has been found that cylindrical, square and rectangular shaped tablets do not reliably fall into the wash tube from holder when the detergent holder is opened. The tablets of the present invention reliably fall from the detergent holder into the wash tub when the detergent holder of an automatic dishwasher is opened. This particularly is the case for General Electric automatic dishwashers.
This invention is directed to a dishwasher detergent tablet that has a shape that is readily dispensed from the detergent holder of an automatic dishwashing machine into the wash tub at the start of the wash cycle. The shape should be of a generally elliptical to a modified generally elliptical shape. This is an elliptical-like shape where the diagonal dimension of a rectangular cylinder contained within the generally elliptical to modified generally elliptical shape is a minimum. This is a cylinder of rectangular cross-section that has a maximum volume with respect to the volume of the tablet. The diagonal dimension is the diagonal of a rectangular cross-section along the minor axis. This further will aid in providing a non-stable shape for the detergent tablet. A generally elliptical shape can be one defined by the formula:                     (                  x          a                )            p        +                  (                  y          b                )            p        =  1
where 2a is the length of the major axis, 2b is the length of the minor axis, and p in an exponent. The exponent p should be from about 1.5 to about 25 and preferably about 2 to about 20. This will produce a generally elliptical tablet. As the value of the exponent p increases, the generally elliptical shape approaches a modified generally elliptical elongated bar-like shape. In this latter shape the sides of the tablet along the major axis can be essentially parallel with sides along the minor axis curved, and preferably a compound curve.
In another preferred embodiment the edges of the tablet also are beveled. This increases the instability of the tablet in the detergent holder. Each edge can be beveled or only one or more edges can be beveled. Further, the bevel need not be of the same dimension fully around the tablet. The bevel on one or more sides of the tablet can be of a greater or lesser dimension. The objective is to have a shape that is not stable in the detergent holder. The shape should be such that the tablet tends to fall toward and into the wash tub upon the dispenser holder being activated.
In a further preferred embodiment at least one of the top surface and the bottom surface is convex in shape. Most preferably both the top surface and the bottom surface are convex in shape. Convex shapes will add to the instability of the tablet in the detergent dispenser. Such a shape also fits well into the detergent holder and does not interfere with the opening of the detergent holder.
The tablet can be a mixture of these features. It can be flat on a bottom surface and convex on a top surface. The particular design features are chosen to meet particular requirements.
The tablet can be of a single layer or of a multilayer structure. For instance the outer layer can be detergent and an inner layer can be a bleach. The detergent layer also can contain enzymes. When a bleach is a part of the tablet, preferably it is the inner layer sandwiched between two outer detergent layers. This is the case since a bleach layer has a tendency to absorb moisture and decrease in strength. It is protected when sandwiched between detergent layers. Further, a bleach can be harsh on hands, and since the tablet is to be handled, it is preferred that it can be in a configuration to minimize skin contact with the bleach component.
In an additional preferred embodiment the different layers of a multilayer tablet will be of different colors. This would assist in informing the user that the tablet is comprised of more than one component.